Optical recording/playback of information has been made possible by developments in the areas of lasers and thermal recording media. Recent developments have led to mass data storage systems utilizing a plurality of individually modulated laser beams to record information at extremely high data rates. For example, in U.S. Pat. No. 4,449,212, issued May 15, 1984, to C. W. Reno, a multi-track record/playback apparatus is described. In the Reno patent the light beam from a single high power laser is split into a plurality of beams which are individually modulated and focused on the surface of a recording medium. In general, systems of the Reno type use large, high power lasers which require external cooling. Furthermore, in these systems a modulator is provided to individually modulate each beam of the multiple beams being used for recording. For these reasons, prior art multi-beam systems tend to be bulky, low in efficiency, and difficult to modulate.
The development of semiconductor laser arrays is the first step to multi-channel optical recorders/players which overcomes some of the problems of the prior art multi-channel systems. The use of a monolithic array of high-power, single-mode diode lasers, which can be modulated directly and independently, represents a significant advance toward the realization of compact, efficient, high-performance recording systems.
Lasers operating reliably at high power (&gt;20 mW at 50% duty cycle) in a stable fundamental spatial mode are required for high-data-rate optical recording. The most powerful commercially available semiconductor device having these attributes is the constricted double heterojunction large-optical-cavity (CDH-LOC) AlGaAs laser. In an array of CDH-LOC lasers, the devices may typically be separated by only 150 .mu.m.
The use of a diode laser in a high-speed optical recording/playback system requires that the laser be biased with a current which is smaller than the laser threshold, the point above which the lasing action starts. This is necessary to minimize the delay between the input of the modulating signal to a laser and the corresponding light output from the laser. Thus, a driver circuit for use with a diode laser at the high recording speeds contemplated must include means for providing a bias current through the laser. The present invention relates to a driver circuit for use with a CDH-LOC laser diode array which provides bias currents through the laser diodes and which provides the necessary drive currents to the anode (p side) of the diodes to modulate the lasers, while maintaining electrical isolation between the diodes and further maintaining a suitable thermal and mechanical enviroment.